delete the mappings ledger — per-job in-memory resolution + notes fingerprint guard

The persisted (chatId, sourceId)→node table was a shared namespace across
independent chunk/batch jobs: each chunk's extractor mints local ids fresh
(p1..pN), so later chunks collided with earlier ones — propositions silently
skipped as 'already resolved' (coverage checkpointed anyway: permanent silent
loss) and edges resolved onto the wrong nodes (the 'everything links to
everything' mush). Owner ruling 2026-09-29: mergeFindings resolves THIS job's
ids in memory, nothing persists between jobs; cross-job identity is the
auditor's linkTo verdicts alone.

- contracts: NodeMapping dies; NotesSource.contentFp — sha256 of the text at
  the last run, the re-import guard (unchanged re-import = TRUE no-op, no
  model calls, no usage; changed text re-runs; legacy unstamped sources
  re-run once)
- merger: job-local resolution map, in-submit duplicate ids skip once,
  edges resolve extractor-local ids only
- ports/store: appendMapping/readMappings, LEDGER_FILES.mappings,
  rewriteLedgers.mappings gone (stale data/graph/mappings.jsonl just stops
  being read)
- session-clusters: birthSessionOf is provenance-only — the legacy
  mapping-line fallback for provenance-empty notes nodes dies
- deletion: no mapping rows to strip; stats lose mappingsRemoved
- replay-layout batches nodes by first provenance point
- graph.test pins the new independence semantics (re-merge re-creates;
  duplicate ids within one submit resolve once); extraction tests pin
  per-chunk merges + the fingerprint guard

src/agent/subagents/extraction.ts

@@ -1221,11 +1221,19 @@ export function createExtractionPipeline(deps: ExtractionPipelineDeps): Extracti
 
 	/** Import ONE raw notes file: register the source (deterministic id per
 	 *  file path — re-import keeps the same identity and its usage history)
-	 *  and run the pipeline over it. */
+	 *  and run the pipeline over it. Re-import guard (owner, 2026-09-29):
+	 *  the file's content fingerprint decides — unchanged text is a TRUE
+	 *  no-op (the mappings ledger used to dedupe this at merge time by
+	 *  accident); changed text re-runs the whole file. */
 	async function importNotes(input: NotesImportInput): Promise<EmissionStats> {
 		const id = `src_${crypto.createHash("sha256").update(input.filePath).digest("hex").slice(0, 12)}`;
+		const contentFp = crypto.createHash("sha256").update(input.text).digest("hex").slice(0, 16);
+		if (graphStore.readSources().find((s) => s.id === id)?.contentFp === contentFp) {
+			console.info(`[extraction ${id}] re-import with unchanged content (fp match) — skipping`);
+			return { nodes: 0, edges: 0 };
+		}
 		const importedAt = new Date().toISOString();
-		graphStore.upsertSource({ id, filePath: input.filePath, importedAt });
+		graphStore.upsertSource({ id, filePath: input.filePath, importedAt, contentFp });
 		return runNotesExtraction({ id, ...input, importedAt });
 	}